1. Field of the Invention
The present invention relates to a throttle valve controlling apparatus of a motor drive type for opening/closing-driving a throttle valve of an internal combustion engine through a DC (direct current) motor.
2. Description of the Related Background Art
In a conventional throttle valve controlling apparatus of a motor drive type, an accelerator opening degree sensor for detecting a stepping-in amount (accelerator opening degree) of an accelerator pedal, a throttle valve opening degree sensor for detecting a real opening degree of a throttle valve, a DC motor for driving the throttle valve, and a controlling circuit for controlling rotation of the motor are provided (see, for example, Japanese Patent Application Kokai No. 2000-156989). The conventional apparatus sets a target throttle valve opening degree corresponding to the accelerator opening degree detected by the accelerator opening degree sensor, sets a duty ratio based on the difference between the target throttle valve opening degree and the real throttle valve opening degree detected by the throttle valve opening degree sensor, and drives the motor at the set duty ratio. The motor is supplied with a current corresponding to the duty ratio, so that the throttle valve is driven to decrease the difference between the target throttle valve opening degree and the real throttle valve opening degree.
In the conventional throttle valve controlling apparatus, as the DC motor, one which is capable to sufficiently obtain torque required to open or close the throttle valve in a transition operation state such as hard acceleration and hard deceleration of the internal combustion engine is usually used. However, since a DC motor which can satisfy such a condition becomes relatively large, there is a problem that it is difficult to downsize the throttle valve controlling apparatus.